How to get OTP code in SMTP email template

I don't know how to get the OTP code to show in my custom email template for email authentication using OTP.

I have email authentication set up for iOS app, and I'm using resend for my SMTP. Everything seems to work well; the user an receive the email in test, except I don't know what variable (or something else) to use to show the OTP code in the email the user receives.

I customized the email template in Auth -> Templates -> OTP Session.

If we can't get the OTP to show, then the custom template feature for email auth isn't usable. Does anyone know how to solve this?